Mass Transport in the Dehydrogenation Reaction of B$_{20}$H$_{16}$

The compound B$_{20}$H$_{16}$ has been predicted to decompose directly into 20B and 8H$_{2}$ with favorable hydrogen release (6.9 wt. \%) and equilibrium temperature ($T$ = 20 $^{\circ}$C at a pressure of 1 bar H$_2$) [W.Q. Sun, et. al. Phys. Rev. B. \textbf{83}, 064112, 2011]. The segregation of B and H during this reaction is investigated using density functional theory assuming that this process is mediated by the diffusion of native point defects in solid B$_{20}$H$_{16}$. Using the calculated formation energies under relevant chemical conditions, those defects that form in the largest concentrations, and thus those that facilitate mass segregation, are identified. These results are used to gain insight into the possible kinetic limitations of this hydrogen storage reaction.